Method for Disconnecting an Electrical Machine on a Running Gear of a Vehicle, in Particular a Hybrid Motor Vehicle

ABSTRACT

A method for disconnecting an electrical machine connected with the wheels of a vehicle&#39;s drive axle by means of a dog clutch having intermeshing couplers includes, upon receipt of a command to disengage, two successively activated steps. In the first step, a torque equal to a calibrated threshold of a target torque (d) is applied to the electrical machine so to effect a zero torque between the couplers. During this step, a dog clutch actuator is deactivated so to allow the dog clutch to disengage from the electrical machine as quickly as possible. Next, a torque having a value determined according to a slope whose value ranges from the calibrated threshold of the target torque (d) to zero is applied to the electrical machine.

The invention relates to a method and a system for disconnecting an electrical machine from a drive axle of a vehicle, in particular of a hybrid automotive vehicle, when the vehicle is running.

The method and system are particularly suited for a hybrid vehicle which is using a combustion engine in such manner as to make the electrical machine contribute to the traction of the vehicle.

Document FR2723553 divulges for instance an automotive vehicle comprising a selective command system for separate or simultaneous actuation of the electrical and thermal power trains.

Document U.S. Pat. No. 5,403,244 divulges an electrical power train of a vehicle with direct transmission coupling, using synchronization means based on friction plates similar to couplings with clutch plates. Clutch type couplings generate energy losses.

To increase the efficiency, the known state of technology is oriented towards dog clutch type couplings. Document FR20905438 describes a control method employing two dog clutch couplers, whereby a force exercised in translation on one of the dog clutch couplers, in order to bring it closer to the other dog clutch coupler, is modulated in function of different approach phases.

The actual conditions of a running vehicle make it difficult to rapidly disengage the dog clutch without shock. This is the case in all conditions, when the vehicle runs at constant speed, or is accelerating or decelerating.

One goal of the present invention is to provide a simplified disengagement, without a transmission clutch, and which does not require modulation of a force in translation, in particular when the vehicle is running.

To achieve this goal, the invention has as object a method for disconnecting an electrical machine, connected with the wheels of the drive axle of a vehicle, by means of a dog clutch. The method is remarkable in that it comprises two successively activated steps starting from a disengagement request:

-   -   a first controlled step of the connected electrical machine, in         which a torque instruction equal to a calibrated threshold of a         target torque (d) is applied to the electrical machine, in order         to obtain a zero torque exercised between the dog clutch         couplers; and     -   a second controlled step of the connected electrical machine, in         which a torque instruction according to a slope starting from         said calibrated threshold of a target torque and ending with         zero value, is applied to the electrical machine.

In particular, in the first controlled step of the connected electrical machine, a dog clutch actuator is deactivated, in order to allow the dog clutch to disengage as soon as possible.

More particularly, in the second controlled step, said actuator is commanded in order to separate the dog clutch.

Advantageously, said calibrated threshold of a target torque is adaptable with parameters.

The invention has also as object a system for coupling an electrical machine with the wheels of a drive axle of a vehicle when the vehicle runs, comprising:

-   -   an upstream dog clutch coupler which rotates together with the         electrical machine, a downstream dog clutch coupler which         rotates together with the wheels and an actuator arranged for         bringing the two dog clutch couplers closer together in         translation along a common rotation axis; and     -   an electronic device arranged for receiving a disengagement         request, and for controlling the torque of the electrical         machine by applying to it a torque instruction equal to a         calibrated target torque threshold, which results in zero torque         being applied between the dog clutch couplers, then by applying         a torque instruction according to a slope starting with said         calibrated target torque threshold and ending with zero value.

In particular, the coupling system comprises a dog clutch actuator for separating the dog clutch couplers.

Advantageously, said calibrated target torque threshold is adaptable with parameters.

The invention has also as object an automotive vehicle comprising a system according to the invention.

The invention will be better understood, and other goals, characteristics, details and advantages of the invention will become clear during the following explanatory description of a particular implementation mode, actually a preferred mode of the invention, provided as a non-limiting illustrating example, with reference to the attached schematic drawings, in which:

FIG. 1 is a schematic view of a hybrid automotive vehicle comprising a coupling system according to the invention;

FIG. 2 is a schematic view of the coupling system according to the invention;

FIG. 3 is a timing chart for explaining the steps of the coupling method according to the invention.

With reference to FIG. 1, a hybrid type vehicle 10, comprises a power train group 11 arranged for driving two front wheels 14 of vehicle 10, and a power train group 12 arranged for driving two rear wheels 44 belonging to the same rear axle of vehicle 10. The power train group (GMP) 11 comprises in known manner, a combustion engine situated here strictly for illustrative purposes in the front of the vehicle. The power train group 12 comprises an electrical machine 42 connected to wheels 44 by a coupling mechanism 43.

FIG. 2 shows in more detail the power train group 12 of FIG. 1. To lighten up the figure and make it easier to understand, the axis of the electrical machine 42 and the axis of wheels 44 are schematically projected on the same axis 46, above which are simply represented the half parts of the electrical machine 42, coupling mechanisms 43 and a square symbolizing the two wheels 44.

In the coupling mechanism 43, a dog clutch system comprises an upstream dog clutch coupler 51 and a downstream dog clutch coupler 52. The upstream dog clutch coupler 51 rotates together with a gear box 45 connected to the output shaft of the electrical machine 42. The downstream dog clutch coupler 52 rotates together with wheels 44 via a differential mechanism, which balances in known manner, the torque between the wheels 44 of the rear axle, in particular when they spin at different speeds, for instance in a turn.

Dog clutch coupler 51 rotates around axis 46 at a rotational speed which is proportional or equal to the rotational speed of the electrical machine 42, and transmits a torque proportional to the torque generated by the electrical machine 42, while preserving the power supplied by the electrical machine 42 with an efficiency factor resulting from the transmission losses between the electrical machine 42 and the dog clutch coupler 51. The transmission losses in the electrical machine 42 and between the electrical machine 42 and the dog clutch coupler 51 can be represented by a drag torque of the part upstream of dog clutch coupler 51.

Dog clutch coupler 52 rotates around axis 46 at a rotational speed which is a function of the speed of wheels 44. A torque applied on dog clutch coupler 52 is transmitted to wheels 44. When the dog clutch coupler 52 is disengaged from dog clutch coupler 51, as shown in FIG. 2, the wheels 44 can turn or not turn, independently of the rotational speed of the electrical machine 42.

The coupling mechanism 43 comprises an actuator 34 arranged for displacing dog clutch coupler 52 in translation along the axis 46. The opposite faces of dog clutch couplers 51 and 52 are provided with teeth and cavities. The teeth of one dog clutch coupler are dimensioned so that they fit in the cavities of the other dog clutch coupler. In this way, when the teeth of dog clutch coupler 52 are facing the cavities of dog clutch coupler 51, as shown in FIG. 2, actuator 34 can engage dog clutch coupler 52 with dog clutch coupler 51 so that dog clutch couplers 51 and 52 are rotating together around axis 46. An on-or-off position sensor 32 is mounted in the coupling mechanism 43 to detect the fully engaged position of dog clutch coupler 52 in dog clutch coupler 51.

When the electrical machine is connected through the coupling mechanism, dog clutch couplers 51 and 52 rotate together. The teeth of dog clutch coupler 52 are engaged in the cavities of dog clutch coupler 51. When the electrical machine operates in motor mode, it applies a torque to the wheels 44, and the faces of the cavities of the dog clutch coupler 51, of which the normal line is oriented in the direction of rotation, exercise pressure force against the faces of the opposite teeth of dog clutch coupler 52, generating friction forces according to Coulomb's law of friction. Similarly, when the electrical machine 42 is operating in generating mode, it receives a torque from the wheels 44, and the faces of the cavities of the dog clutch coupler 51, of which the normal line is oriented in the opposite direction of rotation, are subjected to pressure forces exercised by the opposite faces of the teeth of dog clutch coupler 52, generating friction forces also according to Coulomb's law of friction. The friction forces, which increase with increasing torque, counteract actuator 34 in the translational displacement of the dog clutch coupler 52 along axis 46, in the direction of disengagement. A solution consisting in dimensioning a favorable form of the dog clutch couplers in order to facilitate disengagement in the presence of a torque, poses a problem of orientation because of the two possible opposite directions of the torque, depending on whether the electrical machine is operating in motor mode or generating mode. Over-dimensioning of actuator 34 in order to overcome the friction forces in translation, has the disadvantage of provoking premature wear of the dog teeth. A specific surface treatment of the dog teeth to overcome wear has the disadvantage of significantly increasing the fabrication cost. As dog clutch coupler 52 is disengaged from dog clutch coupler 51, the contact surface between the teeth decreases so that the pressure forces resulting from the torque, have a tendency of increasing until they provoke rotational slip of dog clutch coupler 51 against dog clutch coupler 52 at the moment that the dog clutch coupler 52 leaves dog clutch coupler 51. The stresses thus generated on the teeth constitute another source of wear, even of fractures. The few phenomena, among others, which are mentioned here, show the difficulty of rapidly disengaging without shock the dog clutch couplers when the vehicle is in a driving situation and the driver commands a decoupling of the electrical machine of the vehicle. The mechanical architecture of the rear axle system does not include a clutch or a synchronizer. The only movement of the system is the translation of one of the dog clutch couplers 51, 52 exercised or actuated by actuator 34.

To remedy this problem, the rear wheel drive axle group comprises an electronic device which controls, as we will now explain, in precise manner the torque of the electrical machine 42 in combination with a sequential control of dog clutch actuator 34 in order to achieve rapid decoupling without shock. The electronic device is connected to actuator 34 and sensor 32 in the coupling mechanism 43. The electronic device is connected also to the electrical machine 42 by a current regulated electrical generator. The electrical generator is for instance supplied in known manner starting from a battery, which is not shown. The electronic device comprises on the other hand electronic circuits for digital or analog processing arranged and/or programmed to execute the process steps which will be explained now with reference to FIG. 3.

To explain the process steps, FIG. 3 shows the status of the different signals in function of time.

Specifically, curve 7 represents the coupling command signal for a vehicle speed greater than or equal to 5 km/h. Up to time a when a decoupling request is received, the process is in the initial stage whereby the dog clutch couplers 51 and 52 are engaged with each other so that the electrical machine 42 is connected to wheels 44. The command signal is represented by a high value on curve 7, followed starting from time a by a low value. It is understood that the high and low values are here pure conventions and that the initial stage can also be represented by a low value of the signal followed beyond a by a high value.

Line d represents a calibrated torque level or threshold co above which decoupling is possible. Advantageously, the value of torque co is adaptable with parameters so that it can be calibrated at a value which cancels the torque at the level of the dog clutch couplers. Typically, the torque with value co is the torque which compensates the drag of the gear box and the torque control uncertainty of the electrical machine.

Curve 1 represents the speed of the wheels 44 at dog clutch coupler 52. In the initial step preceding time a, since the vehicle is driving, an increase of curve 1 denotes for instance a vehicle in acceleration phase. The goal of the method is to permit declutching no matter what the speed variations of the vehicle are during the whole declutching phase.

Curve 2 represents the speed of the electrical machine 42 at dog clutch coupler 51, in other words taking into account the gear ratio of gear box 45. In the initial step preceding time a, the electrical machine 42 connected to the wheels, runs at the same speed as the wheels.

In the initial step preceding time a, the electrical machine is controlled in speed or torque servo mode.

Speed mode servo control of the electrical machine 42 consists in regulating the speed of the rotor of the electrical machine. In known manner, speed mode servo control of the electrical machine comprises in general a first step of speed regulation which generates a current instruction for supplying the electrical machine in such manner as to annul the speed gap between the rotor speed instruction and the rotor speed measurement received in return. The current instruction generated by the first step is applied as input of a second step in which the current instruction is submitted to a limitation of the current absorption and supply capacity respectively of the electrical machine and the source of electrical energy, such as a battery or a set of supercapacitors. The second step performs current regulation of the electrical machine by generating a voltage instruction to be applied to the electrical machine in order to annul the gap between the current instruction received from the first step and a current measurement in the electrical machine received in return. The electrical voltage signal applied to the electrical machine, directly commands an electronic power bridge which modulates the electrical voltage drawn from the source of electrical energy. The current passing through the electrical machine generates then a torque which, in known manner, is proportional with the electrical current at constant excitation. The torque generated in this way allows for imposing to the electrical machine a rotational speed equal to the instruction as long as the current does not reach the limit of current absorption and current supply capacity. In motor mode and in generator mode, the current is respectively positive and negative.

Torque mode servo control of the electrical machine 42 consists in regulating a torque supplied by the rotor of the electrical machine. In known manner, torque servo mode of the electrical machine comprises in general also the first step of speed regulation which generates a current instruction for supplying the electrical machine, which tries to annul the speed gap between a rotor speed instruction and a measurement of rotor speed received in return. However, here the speed instruction is slightly higher, respectively slightly lower, than the expected value of the measured speed, in motor mode, respectively in generator mode, in order not to annul the speed gap as long as the effective measurement of the speed is equal to the expected measurement value. The current instruction generated by the first step is applied as input of a second step in which the current instruction is subjected now to a current limit which corresponds with a torque instruction. As previously, the second step performs a current regulation of the electrical machine by generating a voltage instruction to be applied to the electrical machine in order to annul the gap between the current instruction received from the first step which saturates this time at the limit corresponding with the torque instruction, and the current measurement in the electrical machine received in return. As previously, the electrical voltage signal applied to the electrical machine, directly commands an electronic power bridge which modulates the electrical voltage drawn from the source of electrical energy. The torque then generated by the current passing through the electrical machine, is equal to the torque instruction. The slightly over-speed or under-speed instruction, in case respectively of positive or negative torque instruction, allows for forcing saturation of the current at the limit corresponding to the torque instruction. In this way, in case the electrical machine is put accidentally in mechanical freewheeling mode, its rotational speed remains close to the expected speed measurement without falling outside a tolerance range in over-speed and under-speed, because reaching one or the other has the effect of annulling the speed gap and consequently of naturally saturating the current regulation loop.

Curve 3 represents a signal generated by the position sensor 32. As previously mentioned, in the initial step which precedes time a, the coupling mechanism 43 is engaged, indicated here by a low value of the signal of curve 3.

Curve 4 represents a torque instruction signal on the electrical machine 42 which, during the initial step of the method, is the instruction required by the operating speed of the vehicle. For instance, in the case of an acceleration of the vehicle illustrated in FIG. 3, the torque instruction on the electrical machine 42 is positive.

Curve 5 represents the effectively generated torque by the electrical machine which can differ from the instruction, for instance in function of the response time constant of the regulation loop of the electrical machine or other factors.

At the time that the decoupling request is received, the method enters a control step during which the electronic device verifies whether the coupling mechanism 43 is engaged or disengaged. In other words, the electronic device verifies if the position sensor 32 indicates an engaged or disengaged position of dog clutch couplers 51 and 52. If after verification of the coupling mechanism, the coupling mechanism is engaged, the method brings the torque instruction to the value co as indicated by curve 4. As indicated above, the value of torque co is the value which compensates the drag losses upstream of dog clutch coupler 51 so that the torque at the dog clutch is almost null at time b.

As long as the dog clutch couplers are engaged, the speed of the electrical machine, indicated by curve 2, follows the speed of the wheels, indicated by curve 1.

As soon as the calibrated target torque threshold (d) is reached at time (b), the electronic control device of the electrical machine, generates an instruction which follows a slope of which the starting point is equal to the calibrated threshold value of the target torque (d) and the end point a null value. As shown on curve 3, in this second torque control step of the electrical machine the dog clutch coupler (52) begins to separate from dog clutch coupler (51), initially in progressive manner, then definitively at time (c). After disengagement of dog clutch coupler (52) from dog clutch coupler (51), the torque generated by the electrical machine is no longer sufficient to drive it, its rotational speed decreases as shown on FIG. 2), essentially driven by its own inertia.

At time c, the position sensor 32 sends the information back “dog clutch disengaged”. The curves (4, 5 and 6) of FIG. 3 correspond to a motor torque of the electrical machine (42), typically in case of an acceleration of the vehicle. It is understood that the positive torque in motor mode is replaced by a negative torque in generator mode, for instance in the case of a deceleration. The curves are then symmetric relative to the time axis. The slopes are inversed so that the slope ends in both cases with zero value at time (c).

In economic terms, the exploitation of the torque control possibilities of the electrical machine at any operating speed, associated with a simplified actuator, and controlled in simple manner in on-or-off mode, allows for a significant reduction of the cost relative to more complex systems.

Although the invention is described in connection with a specific implementation mode, it is evident that the invention is not limited to it, and that numerous variants and modifications are possible without exceeding its scope or intent. Specifically, the electrical power train group can be mounted both in the front and in the rear of the vehicle, on a drive axle which is identical or different from the drive axle that the thermal power train is mounted on. Although not shown on FIG. 2, a gear box can also be placed between the upstream dog clutch coupler and the wheels. The displacement of the downstream dog clutch coupler can be replaced by the displacement of the upstream dog clutch coupler. 

1. A method for disconnecting an electrical machine coupled with the wheels of the drive axle of a vehicle by means of dog clutch couplers, the method comprising two successively activated steps starting from a disengagement request including: a first torque control step of the electrical machine, in which a desired torque is applied to the electrical machine equal to the calibrated threshold of a target torque (d) so to obtain a substantially zero torque difference between the dog clutch couplers; and a second torque control step of the electrical machine, in which a desired torque is applied to the electrical machine follows a slope starting from said calibrated threshold value of the target torque (d) and ending with a zero value.
 2. The method for disconnecting according to claim 1, characterized in that in the first torque control step of the electrical machine a dog clutch actuator is deactivated so as to allow disengagement of the dog clutch as soon as possible.
 3. The method for disconnecting according to claim 2, characterized in that in the second control step said actuator (34) is commanded to separate the dog clutch couplers.
 4. The method according to claims 2 or 3, characterized in that said calibrated threshold of the target torque (d) is adaptable with parameters.
 5. A system for coupling an electrical machine with the wheels of an axle of a vehicle when the vehicle is running, comprising: an upstream dog clutch coupler rotating together with the electrical machine (42), a downstream dog clutch coupler rotating together with the wheels, and an actuator arranged for bringing the two dog clutch couplers together in translation along a common rotation axis, and an electronic device arranged for receiving a decoupling request and for torque control of the electrical machine by applying to it a torque equal to a calibrated threshold value of a target torque (d) which facilitates achieving obtaining a zero torque as between the dog clutch couplers then following a slope starting with said calibrated threshold value of the target torque and ending with a zero torque value.
 6. The coupling system according to claim 5, characterized in that it comprises a dog clutch actuator with which the dog clutch couplers are separated.
 7. The system according to one of claim 5 or 6, characterized in that said calibrated threshold value of target torque (d) is adaptable with parameters.
 8. An automotive vehicle comprising a system according to the invention. 